Fluid processing, particularly control of overall flow behavior, is vital to various industries. For example, how to make plastics melt to flow easily without degradation is the most crucial issue for plastics molding industry. The ability to transport crude oil is not only critical to these companies in that business, but also is critical to the whole society. In modern industry, fluids are extremely diverse in origin and composition, ranging, for example, from fermentation broths and food products to mineral slurries and polymer melts. However, underlying this diversity are certain properties that determine the overall flow behavior. These properties generally include viscosity, pressure, and velocity.
The viscosity of a fluid refers to its resistance to flow, i.e. the "stickiness" of the liquid. For instance, honey has a much higher viscosity than water. In general, the lower viscosity a fluid has, the more easily it will flow. Fluid is classified into two categories according to viscosity: Newtonian fluids and non-Newtonian fluids. A Newtonian fluid such as water has constant viscosity under a certain temperature. A non-Newtonian fluid refers to a fluid whose viscosity is variable under a constant temperature. Plastics melt, crude oil and pulp fall into this latter category. Pressure normally includes static pressure and dynamic pressure. Static pressure comes from gravity or external forces while dynamic pressure largely comes from a fluid's internal velocity inconsistencies. For non-Newtonian fluids, viscosity depends on both temperature and shear or "friction", which is influenced by dynamic pressure and thus velocity inconsistency. Although these properties influence each other, different applications pay more attention to some of them versus the rest.
Various conventional fluid processing techniques have been used to control these physical properties to satisfy industry needs. These techniques include using heat and shear for viscosity control, and using a pump for pressure control and also for velocity control. Though these techniques are widely used, they have their limits that they can not address all the needs, sometimes create problems, and are sometimes too expensive to use. These issues leave the door open for new fluid processing technologies.
By way of example, the petroleum industry is a huge industry that controls the lifeline of our society. The petroleum industry is composed of integrated oil companies and oil field equipment and services companies as well as pipeline, refineries and resellers. Due to the high cost of project implementation and competition, technology plays an important role in this industry.
As a result, fluid handling is a major issue in petroleum industry. Crude oils produced from wellbores are normally very viscous, which creates challenges for both oil recovery and oil transportation. To make this kind of oil flow through an oil pipeline, a high pressure has to be applied to the oil which has to be maintained throughout the entire pipeline. This is very costly and very inconvenient. The high viscosity of oil is one of the major reasons that so many pumping stations are required. An effective way to reduce viscosity would significantly reduce cost. In the past, as illustrated by U.S. Pat. No. 4,945,937, various attempts have been made to lower the viscosity of crude oil. Moreover, while this patent refers to the use of ultrasonic energy in such a process, it turns out that a wax crystal modifier must be added. Moreover, just adding energy to a tank does not significantly alter the physical characteristics of the fluid.
Moreover, a large problem for oil pipelines is oil spill caused by erosion. Localized high dynamic pressure is one of the causes of erosion. How to control dynamic pressure and thus prevent or deter severe erosion presently is an open question.
Another challenge comes from recovering viscous oil from oil wells. Some wells are filled with viscous petroleum liquids such as heavy crude oil and bitumen that makes them not pumpable with conventional pumping equipment. The high cost associated with well drilling makes it highly necessary to find new technologies to solve the problem.
As to papermaking, the paper industry is both energy intensive and capital intensive. The industry requires high capital outlays for mills and equipment. As a slowly moving industry, it is characterized by boom-and-bust periods. No company can respond instantly to increased demand, because construction of equipment and facilities takes at least four years to complete. There is thus a need for new technologies in paper industry.
The paper industry is faced with a number of problems and challenges. Pulp is the basic building block of paper and paperboard products. It is predominately made from wood. Wood pulp, like other types of pulp, is manufactured by separating the wood fibers which are held together by a material called lignin. The fibers can be separated by either mechanically tearing them apart or by chemically dissolving them.
Pulp handling, including manufacturing, transporting and processing, is central to the paper manufacturing process Pulp, with its viscous nature and other properties, requires sophisticated mechanical systems. The current manufacturing system requires large amounts of energy, which are costly and are not necessarily environmentally friendly. Lack of technology innovation makes the industry operate in a non-optimized way. As evidenced by U.S. Pat. Nos. 4,013,506, 5,213,662, 5,705,032, and 5,472,568 in the last 20 years, research has been done on how to handle pulp more efficiently. Still, new technology for pulp handling remains critical, especially with respect to energy and environmental concerns.
Not only are fluid handling efficiencies important to the paper making industry, in the marine field, propulsion and other problems are prevalent. Noise produced by a propeller is one of the sources that expose a submarine to detection. Noise is mainly caused by uneven pressure distribution, which causes a propeller to vibrate in an unwanted fashion. How to control the uneven pressure distribution and thus reduce noise is a challenge in this industry.
Another big concern is that of cavitation. The major problem encountered with cavitation is its violent nature. Upon the collapse of the vapor "cavities" produced by cavitation a small implosion occurs. These implosions can generate tremendous noise and can be violent enough to damage the blade sections, causing accelerated erosion of the blade surface. As well, the presence of the cavities often changes the performance of the blade section unfavorably. For severe cavitation of a propeller under heavy load, the propeller can become substantially enveloped in cavitation causing thrust breakdown of the propeller and thus loss of thrust. Thrust breakdown is one of the factors that limits the maximum speed of a ship. Eliminating or alleviating the severity of cavitation will not only protect the propeller, but also opens the door for increasing ship speed. Cavitation occurs when the local pressure drops below the fluid vapor pressure. By the very nature of lifting surfaces, low-pressure regions occur on the foil surface that at sufficiently high loads will eventually cavitate. Once again, pressure control remains a question.
In another area, the brewing industry is a very old industry. Competition is intense due to its maturity and globalization, and how to lower manufacturing cost by reducing cycle time is thus important. Typically, the brewing process begins when the malt suppliers soak the barley grain in water, thereby facilitating germination. Then the mill uses steel rollers to crack the grain open before it enters the mash tun. In the mash tun, the malts are mixed with warm water. Thereafter, the result is pumped into a lauter tun, where it is sparged with hot water. This helps extract as much of the sugars from the malt as possible. The conversion of proteins and carbohydrates takes 30-60 minutes but the mashing procedure takes 2-3 hours. Then the base of beer is pumped into the brew kettle and moved to a fermentation cellar where it becomes beer. Fermentation may take several weeks or longer. Particle velocity plays an important role in how long each step will take. If particles are moving fast enough, the reaction can be made quicker and easier. To accelerate this process, control of particle velocity will help to accelerate the brewing process.
As to the plastics molding industry, viscosity plays a pivotal role. Traditionally heat and shear are used for viscosity reduction. These two methods can not always provide the required results. With the increasing acceptance of plastics in various engineering applications, there is a need for technologies that can overcome these problems.
The competitive advantage of the plastic molding industry lies in its ability to create complex geometric parts in a very short cycle time. To do this, molders must quickly force molten plastic into a mold and then rapidly cool it until it solidifies. The extent to which this can be done is largely related to viscosity. In general, the lower a material's viscosity, the more easily it will fill a mold. The standard means for lowering a polymer's viscosity is by applying either heat or shear. The effect of heat on viscosity can be seen from a common experience of heating honey to make it thinner. Shear is microscopically equivalent to the friction between molecules. The fact that pulling taffy will make it softer is an example of using shear to reduce viscosity. In a typical manufacturing process, electric heaters are used to control temperature and either an electric or a hydraulic machine is used to introduce shear by applying high pressure on plastics melts.
Unfortunately, with plastics, both methods have drawbacks and limits to their applicability. The problems with heat are a) Heat may cause material degradation; b) Heat can not be used in a mold since the mold must be kept cool; c) Some materials are not sensitive to heat. d) Using heat increases cycle time. Likewise, shear has these problems: a) It may break the molecular bonds and lead to material degradation; b) It requires sophisticated equipment; c) The shear effect happens only in localized small areas in the current manufacturing process.
As exemplified by U.S. Pat. Nos. 5,803,106 and 4,793,954, ultrasonic apparatus has been used to alter the flow rate of melts. However, these systems are not controllable in terms of the energy direction, energy focusing, the waveform of the energy, the amplitude of the energy or frequency, and thus offer only limited advantages. Also the energy injected into the fluid is only at the die orifice making it an extremely localized energy injection.
Another method not often used is to mix the original polymer with low molecular weight material. This usually lowers material strength and impacts end product properties. Due to these limits, there are a number of problems in the plastics molding industry that remain unsolved. Typical problems include: the mold filling problem in which one is unable to fill a mold. Secondly, there are part quality problems involving warping, blushing, material degradation, and melt fracture. There are also process problems involving material burning, and nozzle blocking. Difficulty in processing some large molecular weight materials also has caused problems, as has the incapability of meeting the demands of making large and complex parts. Finally, there is a lack of enough knowledge about viscosity control that makes current mold design provide low yield rates which translate into expense. Most of these problems can ultimately be attributed to high viscosity.